Tilt tray sorters have been available for many years. Such systems are useful in sorting small packages for delivery to different regions, such as zip code areas. Under control of a computer or programmed logic controller, packages may be identified or coded as they enter the system, and then tracked for output at a chute or bin corresponding to the coded destination.
It is known to form a loop of linked carriages running along a loop of track. A human operator or automatic equipment loads items onto trays mounted on the carriages at one point around the loop, and the system automatically tilts the trays at various output locations adjacent to the track to discharge the packages. Many such systems drive the linked carriages by means of a chain or belt drive, which tends to be expensive and noisy. Such systems also occupy a large amount of space, and include complex mechanisms that are relatively difficult to repair.
At a package delivery company, the amount of time a sorter is shut down for repairs has a significant negative effect on the company's ability to meet delivery deadlines. Thus, reliability is a major goal in designing sorting systems. By simplifying mechanical assemblies and providing for easy substitution of failed parts, reliability can be increased and down time reduced. Furthermore, such companies must take steps to reduce noise levels in their facilities as governmental regulations concerning noise become more strict; thus, lowering noise levels in sorting systems is also a major goal.
The sorting system disclosed in U.S. Pat. No. 4,712,965 drives linked carriages around a dual rail track by means of one or more drive carriages. The drive carriages contain motors which derive power for operation from sliding contacts. The motors drive rollers which are pressed against a third rail by the weight of the motor. The carriages are separated by bumpers, and unloading is accomplished by driven conveyor belts mounted on the carriages, rather than by tilting trays.
Another system of looped carriages, but including a tilting tray mechanism, is disclosed in U.S. Pat. No. 5,054,601, which is incorporated herein by reference. The carriages are driven by induction motors positioned beneath the path of the carriages. A conveyor and overhead loader mechanism automatically load the carriages and shaft encoders monitor the speed of the carriages along the looped track. Rollers mounted on the carriages interact with cams provided along the track to unload the trays at their predetermined destination. The loading and unloading functions are under computer control. A latch mechanism holds the trays in a tilted position until they are straightened by a return mechanism.
In those prior art systems which drive a series of carriages by means of a chain or belt positively connected to the carriages, there is no need to link the carriages. In fact they may be spaced apart along the chain to avoid interaction. However, in some prior systems in which the train of carriages has been pulled by a locomotive carriage or by induction, the carriages must be linked. The linkage between carriages is a source of wear and noise. Therefore, a mechanical joint consisting of multiple interacting metal or plastic parts must be designed to reduce friction and possibly lubricated. Even then, the wear and noise problems associated with each linkage can only be alleviated, not eliminated.
Tilting tray sorting systems are also shown in U.S. Pat. Nos. 4,089,404; 5,018,928; and 4,982,828. The latter patent discloses a mechanism which tilts the trays by moving rollers mounted along the track into the path of cam surfaces on the edges of the trays.
A problem with the tilt tray sorters is that the speed of the tilt trays has been the limiting factor on the operation of the lines. The time it takes to tilt the trays and allow the packages to slide off does not permit the system to operate fast enough to run the lines at the higher rates made available by automation and electronic controls. One of the reasons for the slow speed of the tilt trays is the high degree of tilt (20-40 degrees) of the tray required to discharge the items it carries.
Because the mechanical tilt mechanisms used in contemporary tilt trays have not been able to sustain high speed travel, some manufacturers have offered powered discharge of the items with a belt or powered rollers. However, such systems are often expensive and can be unreliable due to power and signal transmission through a rail. There is a need for a more reliable, inexpensive way to provide quick discharge from a sorting system.
Another problem which arises in the field of automatic sorting is how to handle and sort large, irregularly shaped items. The prior systems noted above generally are unable to handle such irregular items.
As may be seen from the foregoing, prior sorting systems are complex both mechanically and electrically, require a relatively large amount of floor space for the volume of items that can be sorted, require significant maintenance, and by their nature are slow and noisy. There has been a need in the art for a sorting system that is simple in construction, is easy to maintain and keep on line, provides a high throughput of sorted items per occupied floor space, and operates at high speed with low noise levels.